<!DOCTYPE html>
<html lang="en">

  <head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>练习二</title>
  </head>

  <body>

  </body>
  <script>
    /* 
    练习二：
    primivatesReferenceType
    */
    var a = 1;

    function fn1() {
      var a = 2;
      var b = '22';
      fn2();

      function fn2() {
        var a = 3;
        fn3();

        function fn3() {
          var a = 4;
          console.log(a, typeof (a)); //a的值 ?  4,Number
          console.log(b, typeof (b)); //b的值 ?  ‘22’,String
        }
      }
    }
    fn1();
  </script>

</html>